Corona-free high voltage cable



April 5, 1966 R. B. M LAUGHLIN ETAL 9 3 CORONA-FREE HIGH VOLTAGE CABLE Original Filed June 23, 1960 \2 @NsuLATme TACKET) FIFTY jl'2 (\NSULHT \NG :mcKET) Wyw :E i Li l-(UNCTUOUS NHTEEIHL) m \\A \2 (msumme :mcm) I J o INVENTOR.

Rowan) E. SmcuaHE Eusseu. B. NcLnueHuN 3,244,800 CORONA-FREE HIGH VOLTAGE CABLE Russell B. McLaughlin and Ronald R. Sinclair, both of Lancaster, Pa., assignors to AMP Incorporated, Harrisburg, Pa.

Original application June 23, 1960, Ser. No. 38,368, now Patent No. 3,152,028. Divided and this application Jan. 31, 1964, Ser. No. 345,833

1 Claim. (Cl. 174120) This application is a division of our parent application Ser. No. 38,368, filed June 23, 1960, for Method of Making a Lead Assembly, now US. Patent No. 3,152,028.

The use of electrical conductors at high altitudes and high voltage presents special problems. Not the least of these is the effect of corona-discharge which is an arcing of the conductor caused by the high voltage and the low dielectric strength of the atmosphere at high altitudes. This phenomenon is responsible for power loss in the circuit. One way to prevent corona-discharge is to insulate the conductor such as by molding an insulation around the outside of the conductor. The disadvantage of this solution is that during assembly and use the surface of the conductor works itself away from the inner surface of the molded insulation thus creating air pockets. These air pockets then set up areas of corona-discharge.

Stranded wire is particularly vulnerable in this respect. This is because the inner surface of the insulation conforms to the lay of the stranded conductor. When the outer surface of the conductor becomes displaced from its conforming inner surface of insulation, the voids forming air pockets are more pronounced.

It is an object of this invention to provide an electrical cable which is corona free at extremely high voltages. It is also an object of this invention to provide a method of making such a cable with the insulation filled with a silicone grease.

Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there is shown and described an illustrative embodiment of the invention; it is to be understood, however, that this embodiment is not intended to be exhaustive nor limiting of the invention but is given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify it in various forms, each as may be best suited to the conditions of a particular use.

FIGURE 1 is a sectional view of a cable connector.

FIGURE 2 is a sectional view illustrating the cable of FIGURE 1.

FIGURE 3 'is a view similar to FIGURE 2 showing the conductor having worked its way away from the insulation to provide air pockets between the conductor and the insulation.

FIGURE 4 is a view similar to FIGURE 3 showing the pockets between the conductor and the insulation filled with silicone grease.

As shown in the drawing, FIGURE 1, the insulated conductor generally indicated by the letter A comprises a central core which is a metallic stranded conductor 10, completely surrounded by an insulating material, e.g. silicone rubber. As shown in FIGURE 2, molding the silicone rubber about the conductor causes the inner surface of the insulation to assume the shape of the outer surface United States Patent of the conductor. The braided stranded conductor forms a plurality of crests and troughs with the insulation forming complementary crests and troughs. The crest of the conductor opposes the trough of the insulation and the trough of the conductor opposes the crest of the insulation.

In usage when an insulated cable is flexed, or otherwise disturbed, the conductor works free from the insulation so that the area forming a trough on the conductor may realign itself with an area forming a trough on the insulation. This forms a void which permits coronadischarge, when a high voltage is passed through the conductor.

As shown in FIGURE 4, filling the air pockets with an unctuous material 14, having high dielectrical strength such as a silicone grease, seals ofl these air pockets, provides a good dielectric insulation, and effectively prevents corona-discharge.

To fill these voids with grease, it is desirable that the central conductor be entirely removed from the center of the insulation. A grease gun filled with the unctuous material is disposed with its nozzle inserted centrally of the insulation sleeve and the grease is discharged into the insulating cover.

In the meantime a receptacle may be applied to the conductor and the unctuous material applied to the recep tacle. A lead wire, which is finer than the cable 10, is applied to the opposite end thereof. The lead wire is then fed through the insulating jacket 12 until it emerges from the other end thereof pulling the cable 10 behind it. The lead is threaded through the core of the cable 12 until the conductor is properly positioned within the insulation sleeve with the receptacle inserted in one end thereof. Suitable caps are placed over each end of the insulating sleeve to prevent discharge of silicone grease. As noted in FIGURE 4 the grease fills the interstices between the stranded cable 10 and the inner surface of the molded silicone 12.

It has been observed that untreated silicone covered cable which is capable of generating corona at 7,500 volts has been improved by this method to a degree wherein it is capable of withstanding 14,000 volts without developing any corona-discharge.

Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments may be made without departing from the scope of the invention. The matter set forth in the fore going description and accompanying drawings is oifered by way of illustration only. The actual scope of the invention is intended to be defined in the following claim when viewed in its proper perspective against the prior art.

We claim:

An electrical lead adapted to carry high voltages with out developing corona discharge comprising a central conductor including a plurality of conductive wires wrapped each about the other so as to be stranded along the length thereof, said wires as stranded forming surface crests and troughs, an insulating sheath surrounding said central conductor along its length, said sheath being comprised of a relatively thick body of soft dielectric material including a central bore along its length of a diameter to grip the wires of the central conductor said sheath having a series of crests and troughs inexactly aligned with the crests and troughs of said wires developing spaces between the sheath inner surface and the wire outer surface, an unctuous material of high dielectric 3 strength in said sheath bore filling the said spaces defined by the said troughs between the surfaces of the wires and the surface of the sheath bore to substantially eliminate air pockets in said lead and effectively prevent corona discharge from occurring as said lead is utilized to carry high voltages.

References Cited by the Examiner UNITED STATES PATENTS 1,995,356 3/1929 Legg 174114 609,366 9/1948 Great Britain.

ROBERT K. SCI-IAEFER, Primary Examiner.

LARAMIE E. ASKIN, DARREL L. CLAY, JOHN F.

BURNS, Examiners.

D. A. KETTLESTRINGS, H. HUBERFELD,

Assistant Examiners. 

